In-situ Synthesis Of Particle Reinforced Aluminum Matrix Composites And Their Mechanical Properties

Particle reinforced aluminum matrix composites are widely used in aerospace,automobile and other fields because of their isotropic,easy to manufacture,high strength,high temperature resistance and other excellent properties.However,the conventional particle addition methods are additive,the size of the reinforcing phase is limited by the initial powder size,rarely less than1 m,there are also problems such as interface reaction between the reinforcing body and the matrix,and poor wettability with the matrix due to the surface pollution of the reinforcing body.In order to obtain fine,dispersed and thermodynamically stable particles and further improve the mechanical properties of aluminum alloy,this paper adopts in-situ synthesis technology to prepare particle reinforced aluminum matrix composites and discusses the mechanical properties of composites prepared under different processes.The main conclusions are as follows:?1?Under vacuum atmosphere of Al-Si alloy in situ synthesis of SiC technology is studied,when the reaction temperature is greater than 900?,the raw material of C source full reaction,can completely into SiC.When the Si content is less than 15 wt%,it is difficult to synthesize SiC.When the Si content increases to 20 wt%,the Al₄C₃ phase disappears,the composite XRD has obvious SiC phase,and the increase of Si content promotes the synthesis of SiC in Al matrix.When the carbon content increases from 3 wt%to 11 wt%,SiC particles can be synthesized in the aluminum matrix.By changing the C content,the SiC synthesis amount can be adjusted,so as to artificially design the required aluminum matrix composites.At low temperature?800??,by extending holding time can also create SiC,but there are by-products such as Al₄C₃,Al₄SiC₄residual.Synthesis of SiC particles increase temperature from 900?to 1200?,the average particle size increased from 1.29?m to 1.36?m,grew up in the aluminum substrate does not take place obvious and reunion.SiC particles were extracted from aluminum matrix.SiC synthesized in situ had lamellar,short rod,irregular block and other morphologies.SiC crystal types with different morphologies were 3C-SiC.The reaction mechanism of SiC synthesis in situ is progressive reaction,and the growth mode of SiC is layer-stacking.?2?SiC/Al-18Si composites with different SiC content were synthesized from aluminium,silicon and graphite powder in situ by cold pressing and vacuum sintering.The phase composition and microstructure of the composites were characterized.The effect of SiC on microstructure,flexural strength and microhardness of the composites were analyzed.The variation of mechanical properties of composites was discussed.It is found that the matrix phase of the composites is Al phase and the second phases are Si and SiC.The fine SiC particles with sizes ranging from 0.2 to 2.8?m synthesized in situ can be dispersed in Al matrix,which means SiC particles have micron and submicron,and own multi-scale characteristics.With the increasing SiC content,the microhardness values of SiC/Al-18Si composites increase.Meanwhile,the average sizes of SiC particles increase from 0.81 to 1.13?m,but they are still uniformly distributed.It is this dimensional stability that makes the hardness of SiC/Al-18Si composites much higher than that of Al-18Si.When the mass fraction of SiC is 30%,the microhardness of the material is the highest,reaching134 HV,which is 88%higher than that of Al-18Si.?3?Al₄SiC₄ and Al₄O₄C hybrid reinforced aluminum matrix composites?Al₄SiC₄+Al₄O₄C/Al-18Si?were prepared by in-situ reaction of melt-casting method.The effects of different carbon content on the synthesis of Al₄SiC₄ and Al₄O₄C particles and the changes of microstructure and mechanical properties of the composites were studied.The results show that with the increase of carbon content,the size of near-spherical Al₄O₄C particles is sub-micron,and the size of irregular flake Al₄SiC₄ particles increases gradually;When the carbon content was 1.5wt%,the tensile strength of the composite was 20%higher than that of the matrix alloy,and the comprehensive mechanical properties were the best.When the carbon content was 2.1wt%,the microhardness was 77 HV,which was 20%higher than that of the matrix alloy.The fracture mode is quasi-dissociation fracture.The brittle flat zone on the fracture surface decreases and a few shallow dimples appear.The strengthening mechanism of composites is mainly load transfer.?4?In order to further improve the density of the composites,SiC/Al₂O₃/Al composites were synthesized in situ by vacuum hot pressing using aluminium powder,silica powder and activated carbon powder.The effects of particle content on the microstructure and mechanical properties of composites were studied.The results show that the second phase SiC particles are irregular polyhedron with a size of about 2 micron and Al₂O₃ particles are regular square with a size of about 1-2 micron.With the increase of particle content,the grain size of composite matrix decreases,and the average grain size increases by107%.SiC/Al₂O₃/Al composites have higher flexural strength and hardness than aluminium alloys through the interaction of second phase particles SiC and Al₂O₃.When 3%SiC/5.1%Al₂O₃/Al composites were synthesized,their comprehensive mechanical properties were the best,bending strength was 193MPa,microhardness was 51 HV,which was 320%and 82%higher than that of pure aluminum.The fracture mode is quasi-dissociation fracture,and the phenomenon of crack deflection and particle pull-out occurs in the material fracture.With the increase of particle content,the brittle flat zone on fracture surface decreases and more fine dimples appear.The strengthening mechanism of composites is mainly fine grain strengthening and load transfer.